1. Field of the Invention
The present invention relates to a communication device and a method used in a wireless communication system, and more particularly, to a communication device and method of handling channel status information for an unlicensed serving cell in a wireless communication system.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3rd Generation Partnership Project (3GPP) Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3GPP as a successor of the universal mobile telecommunication system (UMTS) for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes at least one evolved Node-B (eNB) for communicating with at least one user equipment (UE), and for communicating with a core network including a mobility management entity (MME), a serving gateway, etc., for Non-Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, increases peak data rate and throughput, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint (CoMP) transmissions/reception, uplink (UL) multiple-input multiple-output (UL-MIMO), licensed-assisted access (LAA) using LTE, etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
Network operators propose to offload network traffic of the LTE/LTE-A system to an unlicensed serving cell, to ease load of the network traffic. For example, the eNB may provide services to the UE via the unlicensed serving cell. However, resource (e.g., service) in the unlicensed serving cell is not always available, and it is not easy for the UE to transmit a channel status information (CSI) report for the unlicensed serving cell to the eNB. The transmission of the CSI report for the unlicensed serving cell is even more complicated, when the UE operates on both a licensed serving cell and the unlicensed serving cell (e.g., in the CA case). In addition, resource for reporting the CSI report is usually limited, and collision may occur when multiple CSI reports are to be transmitted via the resource. Thus, the transmission of the CSI report(s) for the licensed serving cell (and the unlicensed serving cell) is thus an important problem to be solved.